Hydraulic stepping motor



June 13, 1961 IN 2,987,889

HYDRAULIC STEPPING MOTOR Filed Dec. 31, 1958 3 Sheets-Sheet 1 Z5 35 az 4 42 TIME I i 5 D/JPAAC'EMEA/T INVENTOR. 0F DETE/VT a/e BI/V/EL P 04am .STEPPl/VG- WHEL-Z TIME 7 BY all} ATTOEWEYJ June 13, 1961 D. P. DARWIN HYDRAULIC STEPPING MOTOR 3 Sheets-Sheet 2 Filed Dec. 51, 1958 June 13, 1961 D. P. DARWIN 9 HYDRAULIC STEPPING MOTOR Fi led Dec. 51, 1958 3 Sheets-Sheet 5 l w. "Hum "m. 44. 64 I Um: p 64 A "L (T55 N f 4 ,-44 66 5a "HIM Uh. h IH|I| l! limited States Patent i) f 2,987,889 HYDRAULIC STEPPING MOTOR Daniel P. Darwin, Endicott, N.Y., assignor to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 31, 1958, Ser. No. 784,106 10'Claims. (Cl. 60--97) This invention relates broadly to a device for converting substantially constant rotary input motion into intermittent rotary output motion, comprising successive increments of such motion interspersed by intervals of no motion.

This invention comprises a motion converter in which a plurality of drive pistons are successively energized into engagement with a toothed stepping wheel on an output shaft to cause that shaft to have intermittent rotary motion. The device is characterized in that means is provided as a part of the toothed wheel and cooperating with the drive pistons to decelerate the toothed wheel and load as the drive pistons approach their limit of operation as determined by the interaction of the driving piston and the toothed wheel. The driving force is applied to the pistons in a manner that the pistons not only drive or advance the stepping wheel, but they also serve to detent the stepping wheel for a predetermined period of time so as to provide intermittent motion. The invention is further characterized in that the drive pistons are lightly spring loaded and are so related to the pressure fluid supply ports that on their outward movement they throttle these ports to retard such movement, and, thereby, prevent overtravel of the pistons.

Other objects of the invention will be pointed out in the following description and claims and illustrated in the accompanying drawings, which disclose, by way of examples, the principle of the invention and the best mode, which has been contemplated, of applying that principle.

In the drawings,

FIG. 1 is a vertical, central, cross-sectional view through the device;

FIG. 2 is a cross-sectional view taken on the line 2--2 of FIG. 1, looking in the direction indicated;

FIG. 3 is an enlarged detail view of the output shaft stepping wheel with some parts in section to show constructional detail;

FIG. 4 is a cross-sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a developed plan view of the fluid pressure distributor valve forming part of the device;

FIG. 6 is a perspective view of the distributor valve;

FIG. 7 is a cross-sectional view taken on the line 77 of FIG. 1, looking in the direction indicated;

FIG. 8 shows a family of curves illustrating the timing of the hydraulic pressure application to the pistons successively; and

FIG. 9 shows a graph illustrating the displacement of the output shaft with respect to time.

The illustrated device comprises a suitably shaped housing 10, FIG. 1, preferably of cup shaped form, closed at its unwalled end by means of a removable cover plate 12, forming a sealed chamber 14 for a suitable hydraulic fluid 16, as for example oil. Within the chamber 14 is a built-up unit comprising a series of plates 22 24, 26 and 32, assembled in face to face relation, and secured to the inner face of the cover 12 by means of machine bolts 54, FIGS. 2 and 7, but not shown in FIG. 1. These bolts merely clamp these plates together to the inside face of the cover 12. For accurate alignment the plates are indexed by means of dowel pins 56, see FIGS. 2 and 7.

, 2,987,889 Patented June 13, 1961 An input shaft 18, FIG. 1, is journaled' in suitable fluidtight bearings, not shown, on the housing 10 at one end and in the plates 22 and 26 at the other end, where again, suitable bearings may be used, but are not shown. As shown, there is formed integral with the shaft 18 pump gear 20 which cooperates with another pump gear 28 journaled in the plates 22 and 26. The gears 20 and 28 operate within a suitably formed cavity in the plate 24 to provide a gear pump. Since gear pumps are known in many forms, no further disclosure with respect thereto seems necessary.

Mounted on or formed integral with the inner end of the shaft 18 is a pressure fluid distributor valve, indicated generally at 30. As clearly shown in FIG. 6, this distributor valve 30 comprises a cylinder 58, provided with a central annular groove walled in at its axial ends by means of the flanges 60 and 62. On the cylinder 58, forming the bottom of the groove, is a rib 64 which is composed of in line portions 64 and axially offset portions 64', all as clearly shown in FIGS. 5 and 6. The external diameter of the rib 64 is the same as that of the end walls 60 and 62. The distributor valve 30 fits in and is rotatably mounted within a cavity, formed in the plate 32, which is of cylindrical cross-section and of an internal diameter substantially the same as the maximum external diameter of the distributor valve 32. As illustrated, the rib 64 has only one axially offset portion 64 but more than one could be used to increase the frequency at which the output shaft 50 is pulsed for a given speed of rotation of the input shaft 18.

The fluid input to the gear pump is provided at the passage 34 formed in the plate 22 and opening at one end into the chamber 14. The output of the gear pump connects to a passage 36 formed in the plate 26. This passage is aligned vvith a pressure fluid supply passage 38 for the distributor valve 30, which passage is formed in the plate 32.

Likewise formed in the plate 32 are three pressure fluid supply passages 40, 55 and 66, extending from the cylindrical space containing the distributor to each of three cylinders A, B and C, formed in the coverplate 12. As illustrated, cylinder B is on a vertical, central axis and A and C are equi-distant angularly on opposite sides thereof and are radially aligned with a common center. As illustrated in FIG. 7, the fluid pressure supply passages 40, 55 and 66 open into the distributor valve chamber at points angularly spaced apart. Each of the passages 40, 55 and 66 are respectively aligned with passages such as the passage 42 in the case of passage '40, so as to supply pressure fluid to the respective cylinders A, B and C. Plate 32 also has'a common pressure fluid exhaust passage 44 which connects the distributor valve chamber with the chamber 14.

Journaled in a suitable fluidtight bearing, not shown, in the coverplate 12, is an output shaft 50, on the outer end of which is an inertia wheel and coupler which may be of any suitable detailed construction. The inner end of shaft 50 is provided with a toothed stepping wheel 48, rotatable in a cylindrical chamber 49 formed in the plate 12, and radially aligned with the cylinders A, B and C. The chamber 49 is filled with a suitable fluid which may be oil of proper viscosity.

In each of the cylinders A, B and C, is a piston assembly 46, as exemplified in FIG. 2 by the drive piston 68in the cylinder C. This piston is provided with a radial pin 70 projecting therebeyond at both ends into slots 71 formed in the plate 12, see'FIG. 1, so as to permit radial movement of the drive piston 68 while preventing rotational movement thereof. The outer end of the piston 68 is recessed to form a seat for one end of the compression spring 74, the outer end of which seats against the end of the cylinder.

The toothed stepping wheel 48 is shown in more detail in FIG. 3. As illustrated, it has nine teeth and associated with each tooth is a dash-pot mechanism for decelerating the stepping wheel and associated load during the latter part of their motion. This decelerating mechanism includes a spring biased decelerating piston 78 which has a sliding fit in a cylinder 76. The piston 78 is provided with a notch 80 on the side, as shown, so as to be limited in its stroke in either direction by a pin 82 mounted in the tooth. The piston 78 is provided with an internal bore to receive a compression spring 84 which biases the piston 78 in an outward direction, and which is provided with a fluid port 86, which communicates the cylinder 76 with the fluid chamber 49. One of the faces of the wedge shaped end of the drive pistons 68, when actuated, engages the face of the decelerating piston 78 to block off or restrict the flow of fluid from the cylinder 76 through the port 86 to the chamber 49. Hence, the free flow of fluid from the cylinder 76 to the chamber 49 through the port 86 is cut off, while a highly restrictive fluid path is developed as fluid essentially leaks by the decelerating piston 78 and into the chamber 49. By this action a retarding torque is developed and applied to the stepping wheel. After the drive piston 68 reaches the end of its stroke as determined by the depth of the tooth of the stepping wheel 49, fluid under pressure is still applied to the piston 68 so as to detent the stepping wheel 48 in fixed position. The period for which fluid pressure is applied after the piston 68 reaches the end of its stroke, determines the period that the output shaft 50 and load 52 is at rest for that particular portion of the cycle.

It will be seen from the above description that this particular form of device gets all of its operating power from the input shaft 18, which can be driven from any suitable power source. The output of the device appears at the shaft 58 and is in the form of intermittent motion, the increments of which can be spaced by periods of no motion of variable length, depending upon factors which will be described later.

It will also be seen that the hydraulic circuit is completely enclosed within the device and, as suggested above, this circuit preferably contains a suitable oil, although various other fluids may be used.

When the input shaft 18 is running at constant rotary speed, the gear pump will be driven thereby, and as a result of its operation in a well known manner will draw the oil from the reservoir 14 through the intake passage 34 of the pump and discharge it under a pressure through its output passage 36. This oil will in turn move through the passage 38 which is a continuation of passage 36, and be discharged into the distributor valve chamber. As shown, the distributor valve 30 rotates with the shaft 18 as it is fixed thereon.

Referring to FIG. 5, it will be seen that rotation of the distributor valve 31} will cause the rectangular ofiset portion 64 of the rib 64 to progressively connect the ports 40, 55 and 66 with the pressure side of the gear pump. As each of the ports 40, 55 and 66 is connected with the high pressure side of the pump the other two are connected to exhaust through the passage 44. The result will be that the pressure from the continuously running gear pump will be successively applied to the cylinders A, B and C, with the result that their associated pistons will be successively urged inwardly radially, see FIG. 2, to cooperate with the shaped teeth of the wheel 48 to cause it to rotate intermittently in a clockwise direction for the form of tooth shown. For example, in FIG. 2 it will be seen that drive piston 68 has completed its inward radial stroke and has dwelled and just thereafter the distributor valve 30' will cut oif the pressure to the cylinder C and supply pressure to cylinder A.

It should be noted that the motion time of the drive piston 68 may be changed or varied with respect to its dwell time by varying the degree of fluid pressure applied thereto, even though the distributor valve 30 is operating at a predetermined cyclic rate. The drive piston 68 in cylinder A is at the high point of the related tooth, and as it moves inwardly radially it will cause the wheel 48 to advance another step and dwell. When the pressure is on cylinder A through the passage 55, cylinders B and C will be exhausting through passages 40 and 66, as stated above.

The size of the pressure supply and exhaust ports can be selected or even be adjusted with suitable throttling valves, not shown, so that the rate of build-up of pressure in the cylinders A, B and C can be varied, with the result that, as illustrated in FIG. 9, a variation in dwell intermediate each increment of advance can'be provided. The length of dwell can be varied by these adjustments, so that the successive increments of movement will occur as determined by the distributor valve 30 but can be varied in duration as operating conditions require.

It may be noted that the input ports to the cylinders A, B and C, as for example the port 42, of cylinder B, are positioned longitudinally of the cylinders in relation to the stroke of the pistons therein, so that as each piston moves outwardly during its exhaust period, it will partial ly close off the associated port to throttle the escape of liquid to exhaust. This may be varied as desired. It may be noted that the springs 74 function to maintain contact between the drive pistons 68 and stepping wheel 48 at all times.

As a matter of fact, the decelerating pistons 78 on the teeth of the ratchet wheel, and the throttling of the exhausted fluid from the cylinders A, B and C form cooperative forces to smooth out the operation of the outward shaft.

It will be apparent from the above description, to those skilled in the art, that the subject matter of this invention is capable of detailed variation without departing from the novelty of the subject matter herein disclosed. For example, more than three piston assemblies can be used to operate the toothed wheel in which event the distributor valve and the arrangement of the pressure supply passages will be accordingly varied, so that the larger number of piston assemblies may be successively actuated. It is also apparent, for example, with slight modification of the geometry of the stepping wheel, that the device would operate with only two of these piston assemblies, as for example the assemblies A and C. In the embodiment illustrated the pressure fluid is supplied to the cylinders A, B and C successively in timed relation, as shown by the pressure curves of FIG. 8, so that as soon as the supply of fluid to one cylinder ceases it is transferred to the next, in the order of actuation.

It should also be noted that there may be occasion to provide the apparatus embodying the present invention without using the decelerating pistons 78. The instances where decelerating pistons would not be required would be where the load is quite light and would not tend to over-drive the stepping wheel, or if a load is to be advanced in veny short incremental steps, whereby the inertia of the load would always be at a minimum.

While there have been shown and described and pointed out the fundamental novel features of the invention as applied to a preferred embodiment, it will be understood that various omissions and substitutions and changes in the form and details of the device illustrated and in its operation may be made by those skilled in the art, without departing from the spirit of the invention. It is the intention, therefore, to be limited only as indicated by the scope of the following claims.

What is claimed is:

1. A hydraulic stepping motor comprising an output shaft carrying a toothed stepping wheel, a plurality of pressure fluid operated pistons for successively advancing said wheel by engagement therewith, a source of fluid under pressure, means including fluid supply and exhaust passages for successively applying pressure fluid to each of said pistons and exhausting it from others to cause movement of the toothed wheel in discrete steps, and means for applying a decelerating torque to said Wheel during each stepping movement.

2. In the combination of claim 1, said last means com prising retarding devices mounted in each tooth of said wheel.

3. In the combination of claim 1, said last means comprising dash-pots mounted on each tooth of said Wheel.

4. -In the combination of claim 1, means for decelerating the return movements of said pistons during a terminal portion thereof.

5. In the combination of claim 1, said first means comprising common fluid supply and exhaust passages for each piston, said passages cooperating with said pistons on exhaust to throttle them.

6. In the combination of claim 1, said pressure fluid applying means causing said pistons to hold said toothed wheel stationary for a period after each stepping movement.

7. In the combination of claim 1, said last means comprising spring biased pistons operating in cylinders formed in the teeth of said stepping wheel, having throttling passages cooperating with said pistons.

8. In the combination of claim 1, said means for applying pressure fluid including a distributor valve.

9. A hydraulic stepping motor comprising an output shaft having a toothed stepping wheel mounted thereon, a plurality of fluid pressure operated pistons adapted to engage and successively advance said stepping wheel, and means including fluid supply and exhaust passages cooperating respectively with said pistons for successively applying fluid under pressure to each of said pistons while exhausting it from the others over predetermined periods of time to successively actuate said pistons so that they drive and detent the stepping wheel in discrete increments.

10. A hydraulic stepping motor comprising an output shaft carrying a toothed stepping wheel, a plurality of pressure fluid operated pistons for successively advancing said wheel by direct contact, a source of fluid under pressure, means including fluid supply and exhaust passages for successively applying pressure fluid to each of said pistons and exhausting it from the others, and means for decelenating the terminal movements of said pistons during exhaust, comprising the positions of said passages in relation to the piston strokes so that the pistons throttle said passages at the ends of the exhausting strokes of said pistons.

References Cited in the file of this patent UNITED STATES PATENTS 1,455,443 Mayer May 15, 1923 2,246,074 Joy lune 17, 1941 2,397,130 Dawson Mar. 26, 1946 2,642,748 Widmer June 23, 1953 

